Black and tan (is that heresy for the Guinness drinkers?)
It's not heresy as long as your "tan" is Harp, not Bass. Otherwise, you're risking a holy war.
That being said, I love both Guinness and Bass Ale, as well as Harp. The Sierra Nevada Pale Ale is very good, as is (IMHO) the Sam Adams Summer. A great choice in the winter (in addition to Guinness) is a good porter (Sierra Nevada makes a good one IMMSMC). The best stout I ever tasted was Harpoon Stout on tap but, alas, I believe the Harpoon brewery (based in Boston) has discontinued it. As was stated above, a good wheat beer is great for the summer. I loved the English bitters I was able to try when I traveled to London a couple of years ago, and Guinness really does taste better in Ireland. Essentially, I love beer.